The latest information from the British authorities reveals the recent leak at Sellafield went un-noticed for at least three months.
It is now thought the pipe at the Thorp nuclear reprocessing plant started to fail as far back as last August.
It broke down last January but was not spotted until this April, despite several opportunities.
This latest information doesn't change the fact that the leak has no health implications for Ireland, but it is raising Government concerns over the plant.
The Minister for the Environment Dick Roche is describing the news as deeply worrying and says it does nothing to put confidence in the Sellafield plant.
He says it is part of an untenable pattern where a serious incident occurs, the investigation reveals failures and weaknesses, recommendations are drawn up and further assurances given the plant is safe.